1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device wherein formation of a bird's beak and a bird's head when a deep oxide film is formed by local oxidation of silicon (LOCOS) is prevented.
2. Description of the Prior Art
Generally, LOCOS is known as a method for partially forming an oxide film on a semiconductor substrate. According to this method, insulating films such as an oxide film and a silicon nitride film sequentially formed on the semiconductor substrate in the order named are selectively etched to form a predetermined opening. The exposed portion of the semiconductor substrate is then chemically etched to form a groove. In this process, however, side etching occurs at the edge of the pattern. When an oxide film is formed in the groove, the oxide film grows vertically and laterally. The oxide film thus extrudes between the semiconductor substrate and the insulating film, resulting in a bird's beak. At the same time, the bird's beak acts to lift the edge of the insulating film, so that a projection called a bird's head is formed thereat. The bird's beak and head are formed since water or oxygen supplied during LOCOS permeates laterally through the oxide film.
A highly integrated and highly precise semiconductor device cannot be formed due to the bird's beak. Disconnections and short-circuiting occur due to the bird's head to cause poor step coverage when a wiring layer is deposited. Thus, the bird's beak and head do not allow preparation of a semiconductor device with high quality and at a high yield.